(i) Technical Field
The present invention relates to semiconductor device fabrication methods, and more particularly, to a method for fabricating a semiconductor device in which a silicon nitride film is formed on a GaN- or InP-based semiconductor layer.
(ii) Related Art
A semiconductor device using a GaN-based semiconductor or an InP-based compound semiconductor layer, which may, for example, be an FET (Field Effect Transistor) such as HEMT (High Electron Mobility Transistor) has attracted attention as high-frequency, high-power amplifier device capable of operating at high frequencies and outputting high power such as an amplifier for use in a cellular phone base station.
Japanese Patent Application Publication No. 2006-278812 (Patent Document 1) discloses an art of forming a silicon nitride film having a composition ratio of silicon to nitrogen of 0.85 to 3.0 on a GaN-based semiconductor layer located between a source electrode and a gate electrode or between a drain electrode and a gate electrode (the above silicon film corresponds to a silicon nitride film having a refractive index of 2.2 or higher and will, hereinafter, be referred to as silicon-rich silicon nitride film).
According to the art described in Patent Document 1, excessive silicon in the silicon-rich silicon nitride film reacts on oxygen in gallium oxide at an interface between the GaN-based semiconductor layer and the silicon nitride film, and reduces the gallium oxide at the interface between the GaN-based semiconductor layer and the silicon nitride film. It is thus possible to suppress the collapse phenomenon that takes place when a high drain voltage is applied.